Space heaters having fuel-fired radiant burners have been used for drying and for heating various enclosures; exemplary of such heaters are those shown in my U.S. Pat. Nos. 3,315,656; 3,797,474 and 3,849,063. In the devices of each of these patents I have employed a thin, radiation-transmissive panel to act as a "window" for transmitting infrared radiation into the space to be heated and also for sealing the combustion chamber which houses the radiant from the space being heated. In the devices of two of these patents, a stream of cooling air is permitted to flow, by convection, downwardly over the generally tilted or upright panels to cool the panels. In the last-named patent, a device is described in which a coolant outside the combustion chamber serves to cool the radiation-transmissive panel.
The devices in which cooling air is moved across a panel by convection must be of fairly large size in order to prevent flue products from mixing with external combustion air. In the device of the last-identified patent, the ability of a coolant adjacent the outer, exposed surface of the transparent panel is limited in its cooling effect by the thickness of the panel, by its dependent location and by its generally poor heat conductivity.
There is a definite need for a radiant heater employing a radiation-transmissive panel which is in close proximity with the radiant to reduce the heater size, and which is yet cooled continuously so as to avoid overheating of the panel. There is also a need for such a radiant heater which may assume somewhat different orientations in a space to be heated without interfering with its operation.